Illuminator for specular measurements

ABSTRACT

A system for detecting reflectance from an image bearing surface in a printer or electronic copier includes an illuminator array, positioned adjacent to the image bearing surface, comprising a plurality of discrete illuminator elements that are spaced in a linear arrangement; a light diffuser positioned between the illuminator array and the image bearing surface, the light diffuser being positioned with respect to the illuminator array to receive the light beams emitted by the illuminator elements and to diffuse the light beams for transmission to the image bearing surface at an incidence angle; and a linear sensor array positioned adjacent to the image bearing surface such that specular and diffuse portions of the light beams reflecting off the image bearing surface at a reflectance angle bearing are received by the sensors.

FIELD

The present disclosure relates to a system for providing specularreflectance of an image bearing surface in a printer.

BACKGROUND

Defects in the subsystems of a xerographic, electrophotographic orsimilar image forming system, such as a laser printer, digital copier orthe like, may give rise to visible streaks in a printed image. Streaksare primarily one-dimensional defects in an image that run parallel tothe process (or slow scan) direction. In a printing system, an imageinput module is used to measure reflection from an image bearing surfaceand from test patches on the image bearing surface. These image inputmodules are often referred to as densitometers, as they detect thedensity or lack thereof of toner on the image bearing surface. Thesemeasured reflections are used in a streak correction methodology in theprinter.

In prior systems, the image input module uses a fluorescent or a raregas lamp for illuminating the image bearing surface and the testpatches. The fluorescent or the rare gas lamp used for illumination is acontinuous source of light in the cross-process (or fast scan)direction. However, the fluorescent or the rare gas lamp is relativelyexpensive.

SUMMARY

In an embodiment, a system for detecting reflectance from an imagebearing surface in a printer or electronic copier is provided. Thesystem includes an illuminator array, a light diffuser, and a linearsensor array. The illuminator array, positioned adjacent to the imagebearing surface, includes a plurality of discrete illuminator elementsspaced in a linear arrangement, where the illuminating elements are eachconfigured to emit a light beam for transmission to the image bearingsurface at an incidence angle. The light diffuser is positioned betweenthe illuminator array and the image bearing surface. The light diffuseris positioned with respect to the illuminator lens to receive the lightbeams emitted by the illuminator elements and to diffuse the light beamsbeing transmitted to the image bearing surface in the linear directionof the illuminator array. The linear sensor array includes a pluralityof sensors positioned adjacent to the image bearing surface such thatspecular and diffuse portions of the light beams reflecting off theimage bearing surface at a reflectance angle are received by thesensors.

In another embodiment, a method for detecting reflectance from an imagebearing surface in a printer or electronic copier is provided. Themethod includes positioning an illuminator array with a plurality ofdiscrete illuminator elements spaced in a linear arrangement adjacent tothe image bearing surface and configuring the illuminator elements toemit a light beam for transmission to the image bearing surface at anincidence angle; positioning a light diffuser between the illuminatorarray and the image bearing surface; positioning the light diffuser withrespect to the illuminator array to receive the light beams emitted bythe illuminator elements and to diffuse the lights beams beingtransmitted to the image bearing surface in a linear direction of theilluminator array; positioning a linear sensor array comprising aplurality of sensors adjacent to the image bearing surface, such thatspecular portions and diffuse portions of the light beams reflecting offthe image bearing surface at a reflectance angle are received by thesensors.

Other aspects, features, and advantages will become apparent from thefollowing detailed description, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will now be disclosed, by way of example only, withreference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, in which

FIG. 1 is a cross-sectional view of an image input module (including theLED illumination system) used in a printer and an image bearing surface;

FIG. 2 is a perspective view of the image input module (including theLED illumination system) used in a printer and the image bearingsurface;

FIG. 3 is a view of the LED illumination system without a lightdiffuser;

FIG. 4 is a view of the LED illumination system with the light diffuser;

FIGS. 5A-5C show graphs for mono color mode illustrating the amplitudeof the Fast Fourier Transform (FFT) of the specular reflectance profilefor an LED illumination system without a light diffuser, an LEDillumination system with a light diffuser, and a lamp-based illuminationsystem;

FIGS. 6A-6B show graphs for blue color mode illustrating the amplitudeof the Fast Fourier Transform (FFT) of the specular reflectance profilefor an LED illumination system with the light diffuser and a lamp-basedillumination system;

FIGS. 7-9 show bar graphs for full page half tone delta-E results formagenta, yellow and black colors;

FIG. 10-13 show graphs for mono color mode and blue color mode for theLED illumination system with the light diffuser and the lamp-basedillumination system as obtained from full page half tone delta-Eresults;

FIG. 14 shows a system in a printer having an illuminator, a lightdiffuser, and a sensor; and

FIG. 15 is a simplified elevational view of basic elements of axerographic color printer, showing a context of the various embodiments.

DETAILED DESCRIPTION

The law of reflection states that the direction of a specular componentof the outgoing reflected light and the direction of incoming light makethe same angle with respect to the surface normal. That is, the angle ofincidence is equal to the angle of reflectance. Specular reflection isthe mirror-like reflection of light from a surface, in which light froma single incoming direction is reflected into a single outgoingdirection. In contrast, diffuse reflection is reflection of light from asurface, in which light from a single incoming direction is reflected inmany directions, due to surface irregularities that cause the rays oflight to reflect in different outgoing directions. The type ofreflection depends on the structure of the surface. For example, in aprinter, the area on the image bearing surface that is covered by thetoner exhibits a higher proportion of diffuse reflection, while the areaon the image bearing surface that is not covered by the toner exhibits ahigher proportion of specular reflection.

An image input module in a printer measures reflections from an imagebearing surface and from the test patches on the image bearing surface.Test patches are predetermined patches of toner periodically transferredto the image bearing surface for calibration purposes. By imaging thetest patches, the printer can evaluate each printed test patch againstits optimal characteristics, and make adjustments to the tonerdeposition functionality of its print engine accordingly. The imageinput module may use these reflections in the streak correctionmethodology of the printer.

The printer generally has two important dimensions: the process (or slowscan) direction and the cross-process (or fast scan) direction. Thedirection in which the image bearing surface moves is referred to asprocess (or slow scan) direction, and the direction in which theplurality of sensors are oriented is referred to as cross-process (orfast scan) direction. The cross-process (or fast scan) direction isgenerally perpendicular to the process (or slow scan) direction.

The image input module comprises an illuminator array, a lens (such as aself-focusing gradient index lens, e.g., a Selfoc® lens) and an imagesensor. The angular distribution of light produced by the illuminator atthe image bearing surface can vary in the fast scan direction, dependingupon the illuminator architecture, particularly in the case of discretelight sources such as LEDS. Under specular conditions, the lightreceived by the image sensor depends upon the angular acceptance angleof the imaging lens. The angular acceptance angle of the imaging lenscan be expressed as ±α, where α may be 5°, 10°, or other predefinedangle which is a fixed property of the lens. In general, light that isincident at an angle of ≦±α relative to the normal to the image bearingsurface (in the fast scan direction) will, under specular reflectionconditions, be reflected at an angle of ≦±α relative to the optical axisof the imaging lens and will be captured by the imaging lens andtransmitted to the image sensor. Light outside that range of angles willnot be transmitted by the lens. At the fast scan locations above, ornearly above, an LED, there is a significant portion of light with anangular distribution within the acceptance angle of the lens, and thespecularly reflected light is transmitted to the image sensor. However,between LEDs, if the gap is large enough, the only light incident on theimage bearing surface has an angular distribution greater than theacceptance angle of the lens, and hence is not transmitted to the imagesensor.

By modifying the angular distribution of light from the light source(s),the quantity of light collected by the imaging lens is substantially thesame at every location in the cross-process (fast scan) direction,independent of whether one is over an LED or in between LEDs.

In addition, the image input module is sensitive to the uniformity ofthe illumination. Since the image input module measures both thespecular reflection from the image bearing surface, which is anindication of the area that is not covered by the toner, and the diffusereflection from the toner on the image bearing surface, which is anindication of the area that is covered by the toner, an importantparameter to detect is the nonuniformity of the specular to diffuseratio (on a pixel by pixel basis). The specular reflectance from theimage bearing surface is the desired signal in these measurements whilethe diffuse reflectance from the toner on the image bearing surface isan unwanted signal. Therefore, to maximize the specular component inrelation to the diffuse component in the optical system of the imageinput module, the uniformity of the illumination in the plane of theilluminator array has to be improved.

The specular reflectance is also particularly useful for the halftonemasking of the image bearing surface. Halftone technique simulatescontinuous tone imagery through the use of equally spaced dots ofvarying size. In halftone techniques, the density of colored dots(typically the four colors, cyan, magenta, yellow and black), within anarea is varied to reproduce any particular shade. Therefore withhalftone, the patches have dots with toner and blank areas between thesedots. If the patches are more dense, i.e., more dots per area coverage,then the specular signal received from the image bearing surface, whichis an indication of the blank areas that is not covered by the toner, isweaker. On the other hand, if the patches are less dense, i.e., lessdots per area coverage, then the specular signal received from the imagebearing surface, which is an indication of the blank areas that is notcovered by the toner, is stronger. As discussed earlier, high specularreflectance represents the blank areas between the dots (as the imagebearing surface has a high specular reflectance).

The uniformity of the illumination in the plane of the illuminatorarray, and particularly in its linear direction, is improved by using alight diffuser to create a curtain of light essentially homogenized inthe direction of the image bearing surface. The diffuser helps to insuremore uniform specular image capture. The diffuser transforms divergentbeams of the light from an illuminator array into a homogenized lightwith high-transmission efficiency.

FIGS. 1 and 2 show an LED illumination system for a specular-mode imagerusing a light diffuser. The system includes an illuminator array 1, alight diffuser 4, an image input module 100 with a lens array 3, and asensor array 2.

The illuminator array 1 has a plurality of discrete illuminator elements110 that are spaced in a linear arrangement within a housing 102. Thehousing 102 of the LED illumination system accommodates the LEDs andsurrounds them. The LEDs are placed on aboard 1A on the base 104 of thehousing 102. A pair of arms 106 extends from the base 104 of the housing102 encapsulating the LEDs there within. The light diffuser 4 isdisposed in a recess 108 located on each of the pair of arms 106. TheLED illumination system thus allows light from the LEDs to exit throughthe housing 102 containing the diffuser 4, achieving highly uniformdiffusion and light emission from the LEDs, thereby obtaining a highlyuniform light source. As such, the specular to diffuse ratio of thelight beam exiting the diffuser can be highly uniform along the lengthof the illuminator array, despite the presence of the gaps between theLEDs.

Preferably, the illuminator elements of the illuminator array 1 are LEDsthat are equally spaced at regular intervals. In an embodiment, the LEDsare spaced about every 4 mm apart in the fast scan direction. In anotherembodiment, the linear LED array could also use more than one row ofLEDs. The combination of a linear array sensor and linear LED arrayallows for high spatial resolution (e.g., 600 spots per inch) in boththe slow scan and fast scan directions. In one embodiment, the LEDarrays could be all one color, e.g., white or of multiple colors, asdescribed in U.S. Pat. No. 6,975,949, incorporated herein by reference.Other discrete light sources are also contemplated, such as fiber opticlight guide tubes.

In an embodiment, the image bearing surface 10 used in the system is ona photoreceptor comprising a belt or a drum configuration. However, itmay also be the printed document, or any other surface bearing an image.

The light diffuser 4 is positioned between the illuminator array 1 andthe image bearing surface 10. The light diffuser 4 is positioned withrespect to the illuminator array 1 to receive the light beams emitted bythe illuminated elements of the illuminator array 1. The light diffuser4 homogenizes and directionally shapes the light beams coming from theilluminated elements preferably with high-transmission efficiency. Thelight diffuser can be made of any light-diffusive material, such aspolycarbonate or other plastic material. In one embodiment, the lightdiffuser, for e.g., 60⁰X1⁰, is used. The 60⁰X1⁰ nomenclature specifiesthe angles of diffusion in two perpendicular directions. There are avariety of angles of diffusion that can be specified for the twodirections. The “60” degree diffusion is oriented in the fast scandirection (which is also the linear direction of the illuminator array),and the “1” degree diffusion is oriented in the slow scan direction. Anyhigh ratio of diffusion in the fast scan direction to diffusion in thelow scan direction may be used. For example, ratios of 10⁰:1⁰, 20⁰:1⁰,30⁰:1⁰ or higher, including the exemplary 60⁰:1⁰ may be used. Suitablediffusers of this type which are used in the current system areavailable as LSD® Light Shaping Diffusers from Physical Optics Corp.

Other factors, such as the distance of the light diffuser 4 from the LEDarray 1, and/or the orientation of the diffusing surface of the diffuserrelative to the LED are taken into account to reduce the diffuse tospecular non-uniformity. For example, in one embodiment, a distance ofabout 5 mm (for the 60⁰X1⁰ diffuser) was maintained between the LEDarray 1 and the diffuser 4. For example, in one embodiment, thediffusing surface faces the illuminator array.

The lens array 3, such as a Selfoc® lens or other micro lens arrangementwith a predetermined acceptance angle α, is interposed between the imagebearing surface 10 and the sensor array 2. A Selfoc® lens is a gradientindex lens which consists of fiber rods with parabolic index profile. Inone embodiment, the Selfoc® lens has an acceptance angle α of about ±9degrees.

FIG. 14 shows a schematic illustration of the LED illumination systemfor a specular-mode imager using a light diffuser. As mentioned above,the system has an illuminator array 1, a light diffuser 4, a lens array3, and a sensor array 2. In one embodiment, the LEDs 110 are placed on aboard 1A.

The illuminator array 1 is located on a line B-C and is configured toemit a light beam that passes through the light diffuser 4. The lightdiffuser 4 is also located on the line B-C. The light beams from thelight diffuser 4 are incident onto the image bearing surface 10 at pointC, which is reflected, thereby producing generally specular reflectancein a first direction along line C-A, and some generally diffusereflectance at least. The angle (∠ACD) between line A-C and normal lineD-C is substantially equal to the angle (φBCD) between line B-C andnormal line D-C, such that the illuminator array 1 is configured to emita light beam onto the image bearing surface 10 at point C, therebyproducing a generally specular reflectance from the image bearingsurface 10 at a specular reflectance angle along line A-C. The linearsensor array 2 is positioned adjacent to the image bearing surface 10and is located along line A-C, such that it captures the generallyspecular portion and the generally diffuse portion of the diffused lightbeam reflecting off the image bearing surface 10 at a specularreflectance angle at point C. This embodiment provides full resolutionimages for both types of reflected light. A calibration procedure couldbe determined so that the signals from the linear sensor array 2 can beused to work out the true specular reflectance and the differencebetween the specular and diffuse reflectances of the image beingmeasured. For example, the amount of diffuse light being reflected atthe specular angle is determined and the subsequent specular sensorreadings are corrected by subtracting a fraction of the diffuse sensorsignal from the specular sensor signal as discussed in U.S. patentapplication Ser. No. 11/944,243), herein incorporated by reference. LineC-D represents a normal line to the surface at a point C of the imagebearing surface 10. Point C may actually be a line or a region on thesurface of the image bearing surface 10.

Preferably, the linear array sensor is, for example, a full width array(FWA) sensor. A full width array sensor is defined as a sensor thatextends substantially an entire width (perpendicular to a direction ofmotion) of the moving image bearing surface. The full width array sensoris configured to detect any desired part of the printed image, whileprinting real images. The full width array sensor may include aplurality of sensors equally spaced at intervals (e.g., every 1/600thinch (600 spots per inch)) in the cross-process (or fast scan)direction. See for example, U.S. Pat. No. 6,975,949, incorporated hereinby reference. It is understood that other linear array sensors may alsobe used, such as contact image sensors, CMOS array sensors or CCD arraysensors.

In one embodiment, the sensor array 2 includes a specular reflectancesensor array and a diffuse reflectance sensor array as discussed indetail in U.S. patent application Ser. No. 11/783,174), hereinincorporated by reference.

FIGS. 3 and 4 show the illuminator array without and with a lightdiffuser. As shown in the FIG. 4, when the light diffuser 4 is placed ontop of the light emitting diodes 110, a fairly homogenized irradiance isobtained, particularly in the linear direction of the illuminator array.The light diffuser 4 homogenizes or makes more uniform anynon-uniformity from the spacing of LEDs 110 (e.g., areas where the LEDsare very close and overlapping light beams are concentrated, or areaswhere the LEDs are so far apart that darker regions are noticeable). Theparticular diffuser used, for example, in this present disclosure is aLight Shaping Diffuser (LSD), which is discussed in detail earlier.Plastic or ground glass diffusers could be used as well, the choice ofdiffuser is dependant on the use and other parameters of a system, suchas the distance of the diffuser from the illumination array. Asdiscussed earlier, the position of the light diffuser 4 from the LEDs110 optimizes homogenization of the light reaching the image bearingsurface 10 (as shown in FIGS. 1 and 2).

FIGS. 5A-5C and FIGS. 6A-6B show Fast Fourier Transform (FFT)representation of the measured values that are obtained from rawprofiles sensed by the sensor in the image input module. Thestreak-correction system may be operated in a special mode so thatmeasured values can be obtained from the raw profiles as sensed by thesensor. In contrast, FIGS. 8A-8D show Fast Fourier Transform (FFT)representation of the measured values that are obtained from the printprofiles for the streak correction system. In FIGS. 8A-8D, the measuredvalues are obtained from a xerographic print. Hence the scale of theamplitude in FIGS. 5A-5C and FIGS. 6A-6B, is different from the scale ofthe amplitude in FIGS. 8A-8D.

FIGS. 5A-5C show graphs for mono color mode illustrating the amplitudeof the Fast Fourier Transform (FFT) of the specular reflectance of anLED illumination system without a light diffuser, an LED illuminationsystem with a light diffuser, and a lamp-based illumination systemrespectively. The graphs illustrate the spatial frequency incycles/millimeters on a horizontal x-axis. On a vertical y-axis, thegraphs illustrate amplitude of the Fast Fourier Transform (FFT) of thespectral reflectance, which is represented as a normalized reflectancevalue. As shown in FIG. 5A, the spikes in the profiles is due to variousfactors, such as LED frequency, Selfoc® frequency etc. The amplitude ofthe Fast Fourier Transform (FFT) of the spectral reflectance in theplots shown in FIGS. 5B and 5C appear to be same for the LED with thediffuser and for the lamp. By comparing FIGS. 5A and 5B, the spikes inthe FFT profiles due to LED frequency and/or Selfoc® frequency(approximately 0.25 and 0.5 cycles/mm, respectively) were reduced oreliminated by use of a light diffuser.

FIGS. 6A-6B show graphs for blue color mode illustrating the amplitudeof the Fast Fourier Transform (FFT) of the specular reflectance for anLED illumination system with the light diffuser and a lamp-basedillumination system. The graphs illustrate the spatial frequency incycles/millimeters on a horizontal x-axis. On a vertical y-axis, thegraphs illustrate amplitude of the Fast Fourier Transform (FFT) of thespectral reflectance, which is represented as a normalized reflectancevalue. The amplitude of the Fast Fourier Transform (FFT) of the spectralreflectance in the plots shown in FIGS. 6A and 6B appear to be same forthe LED illumination system with the diffuser and for the lamp-basedillumination system.

FIGS. 7-9 show bar graphs for full page half tone delta-E results formagenta, yellow and black colors. A spectrophotometer measures color andprovides the results of the measurements in a format known as L*a*b* or,more simply, Lab. L*a*b* is a three-dimensional color space where L* isthe luminance of the sample, and a* and b* are the color components ofthe sample. If a* and b* are both zero, the result is a neutral color.If two colors are measured using a densitometer and the L*a*b* valuesare plugged into the following formula:

dE ²=(L1−L2)²+(a1−a2)²+(b1−b2)²

The resulting number is referred to as Delta-E or the color difference.

As shown in FIGS. 7-9, the bar graphs illustrate the cells of a testmatrix on a horizontal x-axis. On a vertical y-axis, the bar graphsillustrate Delta-E values. In the bar graphs, the mono channel respondsto light of all wavelengths, while the blue channel responds only tolight near 450 nanometers. As shown in the TABLE 1, the test matrixincludes cells 1-8. The cells 1, 4, 5 and 8 are the cells where thestreak-correction system of the printer is turned off. The cell 2 is thecell where the streak-correction system is turned on, the color mode ismono and the illuminator used is the plurality of LEDs. The cell 3 isthe cell where the streak-correction system is turned on, the color modeis blue and the illuminator used is the plurality of LEDs. The cell 6 isthe cell where the streak-correction system is turned on, the color modeis mono and the illuminator used is the lamp. The cell 7 is the cellwhere the streak-correction system is turned on, the color mode is blueand the illuminator used is the lamp. As shown in FIG. 7, theperformance of the LED in magenta delta-E plot was comparable to theperformance of the rare gas lamp. As shown in FIG. 8, the performance ofthe LED in yellow delta-E plot was an improvement over the performanceof the rare gas lamp for mono mode, and the performance of the LED inyellow delta-E plot was slightly better than the performance of the raregas lamp for blue mode. As shown in FIG. 9, the performance of the LEDin black delta-E plot was comparable to the performance of the rare gaslamp, with the performance slightly better in the mono mode than in theblue mode.

TABLE 1 Cell Illuminator Streak Correction System Color Mode 1 LED OFFMONO 2 LED ON MONO 3 LED ON BLUE 4 LED OFF BLUE 5 Lamp OFF MONO 6 LampON MONO 7 Lamp ON BLUE 8 Lamp OFF BLUE

FIGS. 10-13 show graphs for mono color mode and blue color modeillustrating the amplitude of the Fast Fourier Transform (FFT) of the L*profile of a xerographic print for an LED illumination system with thelight diffuser and a lamp-based illumination system. These graphs areanother representation of the values obtained from full page half tonedelta-E results that are also shown in FIGS. 7-9. The graphs illustratethe spatial frequency in cycles/millimeters on a horizontal x-axis. On avertical y-axis, the graphs illustrate amplitude of the spectralreflectance, which is measured in as a normalized reflectance value. Theamplitude of the Fast Fourier Transform (FFT) of the L* profile of axerographic print in the plots shown in FIGS. 10 and 12 is roughly thesame for the LED illumination system with the diffuser and for thelamp-based illumination system in mono color mode. Similarly, theamplitude of the Fast Fourier Transform (FFT) of the L* profile of axerographic print in the plots shown in FIGS. 11 and 13 is roughly thesame for the LED illumination system with the diffuser and for thelamp-based illumination system in the blue color mode.

A processor (not shown) is provided to both calibrate the sensor and toprocess the reflectance data detected by the linear sensor. It could bededicated hardware like ASICs or FPGAs, software, or a combination ofdedicated hardware and software. For the different applications thebasic algorithm for extracting the specular and diffuse components wouldbe the same but the analysis for the particular applications would vary.

FIG. 15 is a simplified elevational view of basic elements of a colorprinter, showing a context of the present disclosure. Specifically,there is shown an “image-on-image” xerographic color printer, in whichsuccessive primary-color images are accumulated on a photoreceptor belt,and the accumulated superimposed images are in one step directlytransferred to an output sheet as a full-color image. In oneimplementation, the Xerox Corporation iGen3® digital printing press maybe utilized. However, it is appreciated that any printing machine, suchas monochrome machines using any technology, machines which print onphotosensitive substrates, xerographic machines with multiplephotoreceptors, or ink-jet-based machines, can beneficially utilize thepresent disclosure as well.

Specifically, the FIG. 15 embodiment includes a belt photoreceptor 210,along which are disposed a series of stations, as is generally familiarin the art of xerography, one set for each primary color to be printed.For instance, to place a cyan color separation image on photoreceptor210, there is used a charge corotron 12C, an imaging laser 14C, and adevelopment unit 16C. For successive color separations, there isprovided equivalent elements 12M, 14M, 16M (for magenta), 12Y, 14Y, 16Y(for yellow), and 12K, 14K, 16K (for black). The successive colorseparations are built up in a superimposed manner on the surface ofphotoreceptor 210, and then the combined full-color image is transferredat transfer station 20 to an output sheet. The output sheet is then runthrough a fuser 30, as is familiar in xerography.

Also shown in the FIG. 15 is a set of what can be generally called“monitors,” such as 50 and 52, which can feed back to a control device54. The monitors such as 50 and 52 are devices which can makemeasurements to images created on the photoreceptor 210 (such as monitor50) or to images which were transferred to an output sheet (such asmonitor 52). These monitors can be in the form of optical densitometers,calorimeters, electrostatic voltmeters, etc. There may be provided anynumber of monitors, and they may be placed anywhere in the printer asneeded, not only in the locations illustrated. The information gatheredtherefrom is used by control device 54 in various ways to aid in theoperation of the printer, whether in a real-time feedback loop, anoffline calibration process, a registration system, etc.

Typically, a printer using control systems which rely on monitors suchas 50, 52 require the deliberate creation of what shall be heregenerally called “test patches” which are made and subsequently measuredin various ways by one or another monitor. These test marks may be inthe form of test patches of a desired darkness value, a desired colorblend, or a particular shape, such as a line pattern; or they may be ofa shape particularly useful for determining registration of superimposedimages (“fiducial” or “registration” marks). Various image-qualitysystems, at various times, will require test marks of specific types tobe placed on photoreceptor 210 at specific locations. These test markswill be made on photoreceptor 210 by one or more lasers such as 14C,14M, 14Y, and 14K. Printing process may be controlled, for example, by aprint controller 200.

As is familiar in the art of “laser printing,” by coordinating themodulation of the various lasers with the motion of photoreceptor 210and other hardware (such as rotating mirrors, etc., not shown), thelasers discharge areas on photoreceptor 210 to create the desired testmarks, particularly after these areas are developed by their respectivedevelopment units 16C, 16M, 16Y, 16K. The test marks must be placed onthe photoreceptor 210 in locations where they can be subsequentlymeasured by a (typically fixed) monitor elsewhere in the printer, forwhatever purpose.

In an embodiment, the linear sensor array 2, as described above, can beplaced just before or just after the transfer station 20 where the toneris transferred to the sheet, for example, on monitors such as 50, 56. Inanother embodiment, the linear sensor array 2, may be placed directly ona printed sheet as the printed sheet comes out of the machine, forexample, on monitor such as 52.

While the specific embodiments of the present disclosure have beendescribed above, it will be appreciated that the disclosure may bepracticed otherwise than described. The description is not intended tolimit the disclosure.

1. A system for detecting reflectance from an image bearing surface in aprinter or electronic copier, comprising: an illuminator arraypositioned adjacent to the image bearing surface, the illuminator arraycomprising a plurality of discrete illuminator elements spaced in alinear arrangement, the illuminating elements each being configured toemit a light beam for transmission to the image bearing surface at anincidence angle; a light diffuser positioned between the illuminatorarray and the image bearing surface, the light diffuser being positionedwith respect to the illuminator array to receive the light beams emittedby the illuminator elements and to diffuse the light beams beingtransmitted to the image bearing surface in the linear direction of theilluminator array; a linear sensor array comprising a plurality ofsensors positioned adjacent to the image bearing surface such thatspecular and diffuse portions of the light beams reflecting off theimage bearing surface at a reflectance angle are received by thesensors.
 2. The system of claim 1, wherein the illuminator arraycomprises a linear LED array, wherein each discrete illuminatorcomprises an LED.
 3. The system of claim 1, wherein the image bearingsurface is on a photoreceptor comprising a belt or a drum.
 4. The systemof claim 1, further comprising a lens placed in the optical path of thelight beams reflecting off the image bearing surface at the reflectanceangle.
 5. The system of claim 4, wherein the lens is a gradient indexlens.
 6. The system of claim 1, wherein the linear sensor array is afull width array (FWA) sensor, contact image sensor, a CMOS array sensoror a CCD array sensor.
 7. The system of claim 1, further comprising aprocessor configured to process the specular and the diffuse portions ofthe light beams reflecting off the image bearing surface and detected bythe linear sensor array.
 8. A method for detecting reflectance from animage bearing surface in a printer or electronic copier, the methodcomprising: positioning an illuminator array comprising a plurality ofdiscrete illuminator elements spaced in a linear arrangement adjacent tothe image bearing surface and configuring the illuminator elements toemit a light beam for transmission to the image bearing surface at anincidence angle; positioning a light diffuser between the illuminatorarray and the image bearing surface; positioning the diffuser withrespect to the illuminator array to receive the light beams emitted bythe illuminator elements and to diffuse the lights beams beingtransmitted to the image bearing surface in the linear direction of theilluminator array; positioning a linear sensor array comprising aplurality of sensors adjacent to the image bearing surface, such thatspecular and diffuse portions of the light beams reflecting off theimage bearing surface at a reflectance angle are received by thesensors.
 9. The method of claim 8, further comprising processing thespecular and the diffuse portions of the light beams reflecting off theimage bearing surface and detected by the linear sensor array.
 10. Themethod of claim 8, wherein the illuminator array comprises a linear LEDarray, wherein each discrete illuminator comprises an LED.
 11. Themethod of claim 8, wherein the image bearing surface is on aphotoreceptor comprising a belt or a drum.
 12. The method of claim 8,further comprising using a lens placed in the optical path of the lightbeams reflecting off the image bearing surface at the reflectance angle.13. The method of claim 12, wherein the lens is a gradient index lens.14. The method of claim 8, wherein the linear sensor array is a fullwidth array (FWA) sensor, contact image sensor, a CMOS array sensor or aCCD array sensor.